In order to begin the combustion process inside a fossil fuel fired combustion chamber, such as that found in industrial and utility boilers, there must be an energy source to begin the self-sustaining combustion reaction of main fuel and air inside the combustion chamber. Current practice is to use a light fuel oil, natural gas, or propane ignitor of a size between input of 0.5 to 20 Million Btu/hr for each of several fuel admission compartments of the combustion chamber.
Ignitors have a dedicated fuel and air supply and an energy source, typically a spark plug, to produce a flame. In operation, fuel and air are introduced to the ignitor and a spark provides the energy to begin a self-sustaining reaction that keeps the ignitor burning. Proof that the ignitor is operating is established through the use of a flame detector, such as a flame rod, a thermal sensing device, or an optical sensor, that is often integral with the ignitor.
Once the ignitor is proven to be operating, main fuel and air for the combustion chamber can be introduced, often after utilizing the ignitor to preheat the combustion chamber. The energy from the ignitor (the ignitor flame), allows the combustion reaction of the main fuel and air to begin. Generally, once the main fuel and air is ignited the combustion reaction is self-sustaining, and the ignitor can be turned off. However, in some cases, such as due to low volatility of the main fuel, it is necessary to leave the ignitor on in order to keep the main combustion reaction continuing. In other cases, ignitors are left to burn continuously, as may be required by safety laws.
For reasons of safety it is important that the ignitor reliably begin burning on command, and that it be able to be confirmed that the ignitor is producing a flame to insure the safe combustion of the main fuel and air. Failure of an ignitor can result in unsafe accumulations of unburned main fuel and air, resulting in massive explosive damage.
In one known type of coal-fired boiler unit, one or more relatively high-capacity oil burners (warm-up guns) are started by one or more oil- or gas-fired ignitors to preheat the combustion chamber. Once the combustion chamber has been brought up to the proper starting temperature, coal nozzles are ignited by the oil- or gas-fired ignitors, or by the warm-up guns themselves.
At higher boiler loads, i.e., when the amount of coal supplied by the coal nozzles is great, the combustion chamber can typically maintain stable combustion of the pulverized coal. However, when the load goes down and the coal supply is thereby decreased, the stability of the pulverized coal flame is also decreased, and it is therefore common practice to use the ignitors or warm-up guns to maintain flame in the combustion chamber, thus avoiding the accumulation of unburned coal dust in the combustion chamber and the associated danger of explosion.
Certain portions of an ignitor mounted in a windbox compartment of a combustion chamber are subjected to relatively high temperatures, typically on the order of 500 degrees Fahrenheit or higher. In some conventional ignitors, there is a risk that an ignitor wire supplying energy to an ignitor spark element may burn up due to the high temperatures, especially when insufficient cooling air is supplied to the ignitor. Recently, a gas-fired ignitor overcoming this problem has been proposed. However, oil-fired ignitors are still subject to this problem. Accordingly, a need exists for an oil-fired ignitor which provides a reliable spark action and which has improved survivability in a high temperature environment.
An ignitor's spray of fuel and air (the combustive mix) is produced by an atomizer. The spray produced by conventional atomizers used in oil-fired ignitors frequently has too many large droplets, resulting in insufficient oxygen at the base of the flame. An insufficient amount of oxygen results in excessive smoke formation, resulting in an unacceptable opacity from the stack. Accordingly, a need exists for an oil-fired ignitor that produces a spray with more available oxygen at the flame base.
Introduced above, conventional ignitors, no matter the type of ignitor fuel utilized, include some sort of flame sensing device which may be mechanical or optical. The output of such a flame sensing device is transmitted to a control room where operational decisions are made based upon the sensed flame. If no ignitor flame is detected when one is expected to be present, repair personnel must service the non-performing ignitor based upon only the information that a flame is not present. Lack of a flame could be due to any one of a faulty ignitor fuel supply, a faulty ignitor compressed air, or a faulty ignitor spark source. Further, a flame could actually be present, and the flame detector itself could be sending a false lack of flame signal. Currently, there is no way for service personnel to know what ignitor component has failed without physically examining that ignitor. Thus, many man-hours are spent attempting to determine the reason an ignitor has failed. If repair personnel had an indication of a reason for failure prior to beginning a repair operation, many of those man-hours could be saved. Accordingly, a need exists for an ignitor which provides information indicating which component has failed.
Aside from an ignitor failure, routine scheduled maintenance of ignitors is typically performed in an effort to prevent failure. A single utility boiler typically can include upwards of 64 individual ignitors that must be maintained. Performing this routine maintenance is both costly and time consuming. That is, each ignitor, whether functioning properly or not, is regularly inspected. If those ignitors that required service could be identified, not only could the time and cost expenses of services all ignitors be saved, but costs associated with ignitor failure, such as boiler down time, could be saved. Accordingly, a need exists for an ignitor in which the necessity of service can be determined prior to failure.